6965
of the more basic compound is always more intense than its parent species. Reactions 1 and 2 both show a negative dk/dEio,, 11 with the change being much greater for the latter reaction. Charge transfer (eq 4)
+ R1'NNO +RzNNO + Ra'NNO.'
RzNNO.'
(4)
proceeds irreversibly from the less basic to the more basic compound. This is in agreement with the expected decrease in ionization potential with increasing length or branching of the alkyl chain. (11) J. Beauchamp and S. Buttrill, J . Chem. Phys., 48, 1783 (1968).
* Address
correspondence to this author.
Stephen Billets, H. H. JaIR,* Fred Kaplan Department of Chemistry, University of Cincinnati Cincinnati, Ohio 45221 Received June 23, I970
Electrical Effect of Free-Radical Groups' Sir: In the course of a study of dialkyl-N-nitrosamines by ion cyclotron resonance we have found a way to estimate the electrical (substituent) effect of groups like .CHzCH2-. In a previous communicationz we have shown that the order of base strengths in the gas phase of a series of compounds RsNNO is R = Me < Et < n-Pr < n-Bu x i-Pr. We have also shown that a rearrangement occurs in the parent ions of these compounds, leading to ions of the structure *CHEHz '"OH+
/
CZH5
and that these ions undergo proton transfer with free nitrosamines. For diethyl-N-nitrosamine reactions 1-3 Me,NNOH+ EtZNNOH+
+ +
Et2NN0
Me2NN0
2
1
PrzNNO
Et2NN0
3 cHzcH,>~~~~+
Et
+
PrzNNO
-
PrzNNOH'
+
EtzNNOH+ (1)
+
Pr2NNOH'
(2)
2
+
R P N N O ]
(3)
4
were observed, among others, but the reverse of reactions 1 and 2 and reaction 4 were shown not to occur. CH2CH2~NNOH' Et'
+
Me2NN0
+
4
Reactions 1 and 2 and their reverse show that the basicity sequence is 1 < 2 < 3, as previously indicated. Reactions 3 and 4 further show that another basicity sequence is 1 < 4 < 3. In other words, replacement of -CzH6 in 2 by .CH2CH2- to give 4 does not alter the (1) This work was performed under NSF Grant No. GP 7551. (2) S. Billets, H. H. Jaffd, and F. Kaplan, J. Amer. Chem. SOC.,92, 6964 (1970).
basicity by more than the difference of the basicities between 1 and 2 or 2 and 3. The same arrangement can be made for the sequence 2, 3, Bu2NN0 (S), and 6, where -C3H6. is probably *CsHs, \
/"O C3H7 6
CH&HCH2-, since this is the species formed by a 6 hydrogen abstraction. The basicity sequences then are 2 < 3 < 5 and 2 < 6 < 5 . This shows that the electrical effects of -CzH4. and -C3H6. lie, respectively, between those of Me and Pr and Et and Bu. Since the difference between Me and Pr is small and that between Et and Bu even smaller, it may be concluded that the effects of -C2H6* and Et are very nearly the same, as are those of -C3H7- and Pr. Similar information on -CH2., -C4Hs. (presumably CH3CHzCHCHz-), and i-C& (presumably H,C(CH3)CH) is not as complete. The reactions observed show that .CH2- is less electron releasing than Et, but not how much less, and that the other two radical groups are more electron releasing than Pr, but not how much more. However, the conclusion suggests itself that each radical group has an electrical effect very nearly the same as that of the corresponding alkyl group. Unfortunately, no information is available on the detailed structure of the free-radical groups. Although it was assumed that the radical site is fl to the amino group, there is no way, at this time, to assure that no internal rearrangement shifting the site has occurred. * Address correspondence to this author.
-
H. H. Jaff&,*Stephen Billets Department of Chemistry, Uirioersity of Cincinnati Cincinnati, Ohio 45221 Received June 23, I970
Borohydride Reduction of +Bonded Organopalladium Complexes in the Norbornenyl-Nortricyclenyl System. Evidence against a Radical Mechanism Sir: Reductive cleavage of d8 or dl0 metal-carbon bonds by borohydride is well known, particularly among compounds of palladium, platinum, and mercury. We now report that in the norbornenyl-nortricyclenyl system, u-bonded organopalladium complexes Ia and IIa are reduced by sodium borodeuteride with complete retention of stereochemistry, and with little rearrangement. By contrast, the mercury analogs of Ia and IIa are known to afford rearranged products from borohydride reduction, apparently uiu radical intermediates. In order to determine the stereochemistry and extent of deuterium substitution in the products by nmr, it was necessary to devise conditions for reduction which avoid hydrogenation of double bonds2 and hydrogen(1) (a) D. J. Pasto and J. A. Gontarz, J . Amer. Chem. SOC.,91, 719 (1969); (b) G. A. Gray and W. R . Jackson, ibid., 91, 6205 (1969). (2) (a) H . Takahashi and J. Tsuji, ibid., 90, 2387 (1968); (b) R . Palumbo, A. DeRenzi, A. Panunzi, and G. Paiaro, ibid., 91,3874 (1969); (c) M. Green and R . I. Hancock, J . Chem. SOC.A , 2054 (1967).
Communications to the Editor
